Dear Ashley Cooper (remember that we like to know who you are and
where you work...)
There is an old README file in this directory
Your_path_to_QE/7.4.1/PW/examples/EXX_example
In this file, that may be not updated since a lot of time, thus
possibly wrong, it is written that:
WHAT PROPERTIES CAN I COMPUTE ?
Energy and forces (thanks to Hellmann-Feynman theorem forces do not
require extra calculations). In principle also stresses but the
corresponding formulas have not yet been coded.
So structural optimization is OK if the cell shape is kept fixed.
Provided that the README is right, you can either fit by hand some
energy vs volume curve performing a series of relax calculations at
different lattice parameters to find the minimum, or you can optimize
your lattice with vc-relax using your favorite GGA functional, and
then relax the obtained structure using HSE. I would do the former in
the case of cubic cells having a single lattice parameter, and the
latter in the case of hexagonal, tetragonal, orthorombic, ...
This said, you can save significant computational resources using
1) ONCV pseudopotentials (look around for the sg15 database) which
should require ecutwfc significantly lower than 140 Ry (it is useless
to specify ecutrho in the case of NC pseudopotentials).
2) ecutfock, a specific cutoff for Fock integrals. You can obtain good
results using ecutfock = 1~2*ecutwfc, with ecutfock closer to
1*ecutwfc that is good enough for geometry optimization and ecutfock
closer to 2*ecutwfc that is good enough for property calculations.
3) ibrav = 0. Don't use it. Exploit lattice symmetry using a
meaningful ibrav = 4 label for hexagonal cells.
HTH
Giuseppe
Quoting Barsha Pal <[email protected]>:
I am trying to optimize an hexagonal unit cell with HSE06 functional. But
the optimization is running for 12 days and still stuck at bfgs step 2,
with scf step count 34, the optimization taking a long time. The input
specifications are:
&CONTROL
calculation = "vc-relax"
restart_mode = "from_scratch"
forc_conv_thr = 1.00000e-04
etot_conv_thr = 1.00000e-05
outdir = "/"
prefix = "hse_opt"
pseudo_dir = "/"
verbosity = "high"
/
&SYSTEM
celldm(1) = 15.36942147
degauss = 1.00000e-02
ecutrho = 560
ecutwfc = 140
ibrav = 0
nat = 12
ntyp = 3
occupations = "smearing"
smearing = "gaussian"
input_dft = "hse"
exx_fraction = 0.25
screening_parameter = 0.106
exxdiv_treatment = "gygi-baldereschi"
x_gamma_extrapolation = .true.
nqx1 = 2,
nqx2 = 2,
nqx3 = 1,
assume_isolated = "2D"
/
&ELECTRONS
conv_thr = 1.00000e-08
electron_maxstep = 300
mixing_beta = 7.00000e-01
diagonalization ='david'
mixing_mode = 'plain'
/
&IONS
ion_dynamics = "bfgs"
/
&CELL
cell_dofree = "2Dxy"
cell_dynamics = "bfgs"
press = 0.00000e+00
press_conv_thr = 0.5
/
K_POINTS {automatic}
12 12 1 0 0 0
ATOMIC_SPECIES
A 1 A.pbe-mt_fhi.UPF
B 1 B.pbe-mt_fhi.UPF
C 1 C.pbe-mt_fhi.UPF
Previously I tried to run with q points 3 3 1 and the optimization was
running at bfgs step 2 for 1 month,
How can I use the functional and reduce the computational time? Please let
me know.
Ashley Cooper
Phd
GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <[email protected]>
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